(Revised Abstract) DESCRIPTION This pilot research proposal is a conceptual break from a thirty year tradition characterizing the properties of single neurons in the inferior parietal lobule with increasingly complex behavioral tasks and analyses designed to isolate particular cognitive functions. Recent optical imaging studies have revealed the presence of multiple different topographic maps across the cortical surface of the inferior parietal lobule. The lowest resolution, and most robust is a representation of orbital gain fields; optic flow appears to be represented within this much as orientation is within retinotopy in V1. The proposal examines these two functions in inferior parietal lobe from a novel perspective- the neural circuit. There is simply no direct evidence in parietal cortex explaining how its sensory and gain field neuronal properties are generated. The molecular genetics of single neurons will be modified to measure the activity of selected neurons and populations of neurons. Standard microscopy will be used for population measures. Two-photon scanning microscopy will be use to directly compare cellular morphology and function. Specific neurons will be identified and studied over many days to assess the stability of their properties. This concept and the techniques for studying the circuitry is completely novel for association cortex; the use of modified molecular genetics of neurons in vivo in behaving animals has not been performed in any cortical area. The impact of these studies will be to open up cortex beyond striate in the behaving animal to circuit level analysis. In principle, the resolution of imaging can be extended to the level of the sub-cellular elements such as spines. In summary, this proposal is designed to understand properties of inferior parietal lobule neurons in terms of underlying neuronal circuits, much as investigators are now successfully exploring the circuit details of orientation tuning and color in primary visual cortex. Although the technical and conceptual issues are difficult, the expertise assembled is appropriate to the task. The successful outcome of these studies will be a substantial advance permitting direct visualization of the sub-cellular, cellular and circuit properties underlying the highest level cognitive functions such as attention, memory, intention and plasticity in the inferior parietal lobule.